Nickel nanocatalyst exsolution from (La,Sr) (Cr,M, Ni)O₃ (M=Mn, Fe) perovskites for the fuel oxidation layer of Oxygen Transport Membranes

La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) and La_0.75Sr_0.25Cr_0.5Fe_0.5O₃ (LSCF) perovskites with partial substitution of the B-site by 5mol% of Ni were synthesized and characterized for the fuel oxidation layer of Oxygen Transport Membranes (OTMs). X-ray diffraction showed that single phase compounds were obtained at 1300oC. LSCM exhibits a rhombohedral structure and LSCF an orthorhombic structure. Both materials retain their structures, after doping the B site with Ni, with small changes on the unit cell parameters. Thermal analysis under reducing conditions was used to investigate the reducibility of these perovskites up to 900oC, which appears to be enhanced by doping with Ni. The formation of Ni nanoparticles (30-50nm) on the LSCM-Ni and LSCF-Ni grains was observed by scanning electron microscopy, after reducing the samples in 5% H₂/Ar at 900oC, indicating possible enhanced catalytic activity and potential benefits for the development of the OTMs. DC Conductivity measurements conducted under a redox cycle, indicate that LSCFNi presents a better redox stability than LSCMNi.